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This paper presents the optimization of stacking sequence of composite laminate adherends in an adhesive single lap joint under bending moment in order to minimize the amount of maximum peel and sh...

Present work studies the interfacial stresses in tubular single-lap adhesively bonded joints, in the presence of an annular defect (void and debond), subjected to an axial load. Using linear elasti...

The effect of the cellular core on the stress intensity factor at the tip of a crack in the adhesive layer of a five-layer sandwich composite beam is investigated. A Nomex sheet is used to model the cellular core with honeycomb, square, and triangular cells. The mechanical properties of these cells are obtained by the finite element analysis supported by theoretical two- and three-dimensional equations. Based on the deduced properties, the load-displacement curve is generated for a sandwich beam under mode I fracture. The numerical findings are validated against available experimental data. It is shown that the lowest values of the stress intensity factor are observed for a core with a honeycomb structure as compared to the other two cell shapes used in this study, which are composed of equilateral triangles or squares. An increase in the wall thickness of the cells leads to an increase in the stress intensity factor.

In this paper, a novel mathematical procedure is proposed which allows for determination of stresses in a defected adhesively bonded single lap tubular joint under torsion. It is assumed that the s...

A comprehensive literature review on the existing analytical models based on different material and geometry behaviors for both single and double-lap joints (as well as others) has been made to ass...

In order to effectively design an energy harvesting system for any specific application, a model that accurately characterizes the energy harvesting parameters is needed. In the present paper a novel magneto-electro-elastic (MEE) cantilever beam has been proposed and modeled as an effective means to increase the harvested electrical power in a vibration-based energy harvesting system. The cantilever beam is composed of a linear homogeneous elastic substrate and two MEE layers with perfect bonds between their interfaces. Using the constitutive equations, Gauss's and Faraday's laws, based on the Euler–Bernoulli beam theory, the coupled magneto-electro-mechanical (MeM) differential equations are derived for a harmonic base excitation in the transversal direction with a superimposed small rotation. The resulting equations are then solved analytically to obtain the dynamic behavior as well as the harvested voltages and powers of the proposed energy harvesting system. Finally, parametric numerical studies are used to examine the effect of excitation frequency, external resistive loads, and material properties on the performance of the MEE energy harvester. The study reveals that the implementation of the coil circuit has resulted in an increase in the total useful harvested power. According to the numerical results, any increase in the Young's modulus and density of the substrate layer (across the ranges that have been studied and while the properties of the MEE layer are kept constant), increases the magnitude of the magnetoelectric harvested power in the unimorph MEE energy harvester system.

The topic presented in this research is the calibration of small-scale parameters of non-classical continuum theories such as nonlocal strain gradient theory, strain gradient theory, stress-driven nonlocal elasticity, and strain-driven nonlocal elasticity. Governing equations of vibrational behavior of circular nanoplate and associated boundary conditions for each method derived using Hamilton's principle. Obtained governing differential equations from non-classical methods were solved using the general differential quadrature rule (GDQR). Then, the first natural frequencies for different radiuses and different size parameters were obtained. On the other hand, the first natural frequencies of circular nanoplates are calculated using molecular dynamics simulation based on AIREBO and Tersoff potentials for different radiuses. Fast Fourier transform (FFT) was utilized to calculate natural frequencies based on the molecular dynamics simulation. Using the accurate size parameter is an important point in the application of non-classical continuum theories. To obtain the size parameters related to different non-classical methods, the results of molecular dynamics compared to those of nan-classical methods and simulated annealing (SA) algorithm optimization technique was utilized. Results show that stress-driven nonlocal, strain-driven nonlocal, and strain gradient methods cannot predict the behavior predicted by molecular dynamics for all ranges of radius. In other words, the responses of these three methods for any value of the size parameters (in some interval radius) and results of the molecular dynamics method are not equal for a few numbers of studied radii. In contrast to these three methods, the nonlocal strain gradient method predicts the results obtained by molecular dynamics well for all radii. The results of this paper are very useful for researchers in the field of non-classical continuum mechanics.

In this paper, hole stress concentrations in long fibers and their surrounding matrix bays is examined in a hybrid composite lamina. It is assumed that all fibers lie in one direction while loaded by a force p at infinity in the direction of fibers. The width of the lamina is considered to be finite and bears a hole as a defect. Due to the presence of excessive shear stress in the matrix bays bounding the hole, a yielded zone of size 2a o is developed around the hole. Shear lag model (SLM) is used to drive the displacement and stress fields. The resulting equations are solved analytically based on boundary and continuity conditions. It is shown that the shape and size of the hole, as well as length of the plastic zone, have considerable effect on stress concentrations within the lamina. Compared to a lamina with a single type fiber, a hybridized model shows lower stress concentrations in High modulus (HM) fibers bounding the hole as opposed to those of Low modulus fibers (LM) subjected to the same condition. Moreover, hole shape and size, ratio of extensional stiffness of LM to HM fibers, and size of the plastic zone seem to have considerable effect on shear and normal stresses in the matrix and fibers, respectively.

This paper presents the stress analysis of rotating nano-disk made of functionally graded materials with nonlinearly varying thickness based on strain gradient theory. The equilibrium equation and corresponding boundary conditions of nano-disk were obtained using Hamilton's principle. Because of the complexity of governing equations and boundary conditions, the equations are solved using numerical methods. Fixed boundary conditions are considered, in the numerical examples. This analysis is general and can be reduced to classical elasticity. The effect of various parameters such as graded index and thickness profile on stresses and high-order stresses were examined. Values of stresses at inner and outer radial are not zero, because stresses at inner and outer radius accumulate with stresses caused by strain gradient theory. Results show that the effects of thickness parameters are greater than the effect of graded index and the difference between the stress predicted by the classical theory and the strain gradient theory is large when the thickness of nano-disk is small.

This study aims to investigate the effect of viscoelasticity of polymeric matrix of composite materials on the transient stress concentration due to a sudden break in its fibers. The fibers were modeled as a linear elastic, and the matrix was modeled as a linear viscoelastic material. A generalized Voigt–Kelvin solid model was employed to model the viscoelastic behavior of matrix. In this study, finite difference method and an innovative semi-analytical method were used. The governing integro-differential equations have been derived by shear-lag theory and have been solved by initial and boundary conditions before and after break occurrence. The governing equations contain an integral term attributing to the viscoelastic properties of the matrix. The same analysis was conducted for the laminae and laminates with fibers arranged in square and hexagonal arrays. Results obtained from the two methods show a relatively good match. The results show that assuming viscoelastic properties decreases the peak of stress concentration factor and increases the steady stress concentration factor. Finally, the effects of size and location of break in the fibers for lamina and laminated composite were investigated.

The aim of the present study was to introduce new crushing mechanisms in terms of crushing modes for estimating the crushing force and absorbed energy of polygonal thin walled metal sections subjected to axial progressive collapse. For this purpose, two models were developed. The first model, which has been extensively used before and named as “plastic hinge model” (PHM), was modified based on new crushing modes; and as the second, a novel model was introduced by the authors named as “induced curvature model” (ICM). The latter model was considered to be more realistic than the former due to consideration of metal sheet curvatures during progressive folding process, as well as including the hardening effect of the material during plastic deformation. All possible crushing modes for a typical polygonal section were considered and discussed by combining different crushing modes of the corner elements. New expressions for the absorbed energies and crushing force were presented based on the resulting crushing modes. To evaluate the validity and efficiency of the proposed models, a detailed FE simulation was conducted using LS-DYNA. Comparison of FEM, PHM and ICM results showed the superiority of the ICM over PHM.

In this paper, the effect of charge/discharge cycles on the electrode containing nano-zirconium oxide, nanoporous carbon black and graphene nanosheets in electrochemical capacitors has been described. Surface morphology and electrochemical performance of the prepared electrode have also been conducted. The electrode prepared from graphene nanosheets (GNS), nanoporous carbon black (NCB), zirconium oxide (ZrO2), and polytetrafluoroethylene (PTFE) in molar ratio of 54:09:27:10 respectively showed a maximum specific capacitance as high as 11.84 F g−1 in the potential range between −0.45 and 0.35 V (V vs. SCE) at a scan rate of 10 mV s−1 in a 3 M NaCl electrolyte. The electrochemical results show the low ratio of the outer to total charge (q⁎O/q⁎T) which confirms the low current response and higher voltage reversal at the end potentials. SEM images confirms the ions re-deposit as agglomerates and accompanied by a drastic decrease in the surface area on the surface of the electrode after one charge/discharge cycle.

In this study, effect of morphology and pore size distribution on physicochemical properties of graphite nanosheets (GNSs)/nanoporous carbon black (NCB)/CeO2 nanoparticle electrodes were investigated in 3 M NaCl electrolyte. 90:00:00:10 (GNS:NCB:CeO2:PTFE) electrodes show a flat and smooth surface and 75:00:15:10 electrodes showed micro pores which opened on surface. In the presence of NCB particles, electrodes like 25:50:15:10 showed the macro, micro and nano pores, simultaneously. Total charge ( q T * ) of 1.73, 37.88, 208.33 C g−1 cm−2 and outer charge to total charge ( q O * /) of 0.53, 0.43 and 0.24 were obtained from 90:00:00:10, 75:00:15:10 and 25:50:15:10 electrodes, respectively. It is concluded that introducing narrower and deeper pores on surface of electrodes increases the charge storage capability and decreases the current response and power delivering capability. Flat surface of GNSs showed 3.4 F/g and also exhibited good capacitance retention of more than 80%. Additionally, nanoporous structures increased the capacitance of 25:50:15:10 electrodes up to 16.2 F/g at 10 mV s−1 in 3 M NaCl electrolyte.

Mechanisms of charge storage, stability, capacitance, morphology and response current of graphene/cerium oxide (CeO2) nanoparticles as an electrode material for electrochemical capacitors have been investigated. Electrochemical properties of the assembled electrodes were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques in 3 M NaCl, NaOH and KOH electrolytes. Scanning electron microscopy (SEM) is used to characterize the microstructure and the nature of prepared electrodes. SEM images confirm the layered structure (12 nm thickness) of the used graphene. The proposed electrode shows a maximum specific capacitance as high as 11.09 F g−1 in the potential range between −0.55 and 0.3 (V vs. SCE) at scan rate of 5 mV s−1. The charge/discharge cycling test shows a good reversibility and confirms that capacitance will increase after 500 cycles by 37%.

The effect of a crack in the overlap region of a single step lap joint is studied on the shear distribution in the adhesive layer. Each adherend is considered to be a lamina with unidirectional fib...

The effect of void shape and volume fraction of fibers on the distribution of stresses in a laminated composite plate subjected to a tensile load applied in the fiber direction is investigated. The cross section of all fibers is triangular. The void can simulate an internal crack or a cylindrical hole. The shear-lag model is used to derive the field equations. By using proper boundary and bonding conditions, complete load and displacement fields in the laminate are determined. The effects of physical parameters of fibers and of void shape and its location on stress concentrations and peak shear stresses in the laminate are studied. The analytical results for stress concentration factors are compared with those given by the finite-element method, and a close agreement between them is found to exist.

In this paper, the effect of ion sizes of cations and anions on the charge storage capability of graphite nanosheets is investigated. Electrochemical properties of prepared electrodes are studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques, in 3 M NaCl, NaOH and KOH electrolytes. A scanning electron microscope (SEM) is used to characterize the microstructure and nature of prepared electrodes. SEM images and XRD patterns confirm the layered structure (12 nm thickness) of the used graphite with an interlayer distance of 3.36 A. The electrochemical results and the ratio of q O ⁎ / q T ⁎ confirm a better charge storage and charge delivering capability of prepared electrodes in 3 M NaCl electrolyte. The charge/discharge cycling test shows a good reversibility and confirms that the solution resistance will increase after 500 cycles.

Nonlinear free and forced vibration behavior of a porous functionally graded Euler-Bernoulli nanobeam subjected to mechanical and electrical loads is studied based on the nonlocal strain gradient elasticity theory. It is assumed that the porous functionally graded (FG) nanobeam is resting on a nonlinear foundation. Also, material properties of the nanobeam are assumed to vary in the thickness direction. Equations of motion are derived using Hamilton's principle. Galerkin method along with variation iteration method (VIM), Homotopy perturbation method (HPM), Hamiltonian approach method (HAM) and multiple scale method are employed to solve the governing equations based on clamped-clamped, simply-simply and clamped-simply boundary conditions. For verification purposes, the results of this study are compared with those of other studies. The effects of different parameters such as type of porosity distribution, nonlinear foundation, boundary conditions, electrical voltage and size effect parameters on the primary and secondary resonances were investigated. It was found that length-scale parameters have a crucial role on the nonlinear vibration behavior of such structures.

In this paper, the effect of viscoelasticity of adhesives on shear stress distribution in the adhesive layer of a single-lap joint under shear load is studied. The joint comprises two elastic single isotropic adherend layers joined by a viscoelastic adhesive polymer. A three-parameter viscoelastic solid model is used to deduce the governing differential equation in the Laplace domain, which is solved using residue theorem. Results show that for an impulse load of 100 N, the maximum shear stress in the adhesive layer is reduced to 39% of its initial value. Also, the ratio of viscous modulus of the adhesive to its shear modulus has an adverse effect on the peak shear stress. An increase in the thickness of the adhesive layer reduced the induced peak shear stress in the joint. Moreover, the shear strain in the adhesive layer reached its steady value after 1000 seconds.

To ensure mechanical integrity, all pressure vessels shall be inspected at the intervals provided in inspection codes or based on a risk-based inspection (RBI) assessment. The RBI assessment may allow previously established inspection intervals to be extended. This paper describes the methodology, analysis and results of two RBI studies conducted on 293 pressure vessel components in two crude oil distillation units. Based on API RBI methodology in API 581 (2008), risk target concept was used for determining inspection dates. It was shown that when thinning is the major active damage, the RBI recommended intervals are as long as twice the API 510 intervals. This paper summarizes that, as a fundamental step in the risk calculation, RBI has a more defined methodology for evaluating equipment for multiple damage mechanisms and a more defined approach to specify the use of other inspection technologies beyond the traditional visual, ultrasonic, and radiography tests.

In this paper, the effect of viscoelasticity of polymeric adhesives on shear stress distribution in the adhesive layer of a double lap joint under shear is studied. The postulated model is composed of three single isotropic adherend layers joined by polymeric adhesives. Each adherend layer is assumed to behave as linear elastic. The results are deduced for epoxy adhesive, and hence, 3-parameters solid model is used to model the viscoelastic behavior of the adhesive layers. The derived equilibrium equations are transformed into Laplace domain and are solved using residue theorem. Results show that for a step load of P 0 = 100 N, the peak shear stress in the epoxy adhesive layer reduces to its steady value over a time span of almost 1000 s. Moreover, if the applied load is raised gradually from zero to its final value of 100 N in seconds, its rate of increase has a direct effect on the peak shear stress developed in the adhesive layers. The influence of the adhesive thickness, as well as the effect of adhes...

In this work, stress distribution in adhesive layers of a double-lap joint subjected to tension and suffering from a void or a partial debond at the adhesive–adherend interface is examined. For symmetric voids, the deduced equilibrium equations are decoupled for better application of boundary conditions at the extreme ends of each adhesive layer. The proposed method of solution has resulted in better estimates on peak shear stress developed in the adhesive layers. The results based on analytical solution are compared with those of finite element findings. Very good agreement is observed between the two. The major difference between stresses stemming from debonds and voids occurs at the edge of the large size defects. For small central defects, it is hardly discernible by the stresses to distinguish the type of defect. Moreover, there appears to be an optimum length to thickness ratio for each adhesive layer which produces minimum peak interfacial shear stress. This value seems to be a function of defect s...

This study compares ball, bar-clip and bar-ball attachment systems for implant-retained mandibular overdentures with three implants. The first implant is placed in the middle of the mandible and the other two are imbedded in the first premolar regions. Linear elastic finite element analysis is used for design analysis. Three dimensional geometry of the mandible is generated from computed tomography. Other parts are modeled using SolidWorks software. The foodstuff is positioned at the right first molar, representing the most frequent masticating situation. To obtain accurate mesh-independent results, finite element models are solved using several mesh grids. They are then validated by means of a detailed convergence analysis. The results demonstrate that the highest von-Mises stress in the bone is always located around the neck of the implant, at its upper threads. Ball and bar-ball attachments transfer the highest and lowest stresses to the bone surrounding the implants, respectively. The lowest stresses in the cortical and cancellous bones are due to bar-ball attachment. Yet, the overdenture gets its maximum movement for this arrangement. Consequently, the use of bar-ball attachment is only recommended for the cases in which stress transferred to peri-implant bone is more important than overdenture stability. Among the three treatment designs, ball attachment seems to exhibit the lowest lateral and overall displacements and hence, better overdenture stability.

In this research the roll steer of a front McPherson suspension system is studied and the design characteristics of mechanism are optimized using Genetic Algorithm method. The roll steer is defined as undesirable and uncontrollable changes in the steering angle of the steered wheels during the rolling action of the vehicle body due to cornering maneuver or asymmetric bumps. The roll steer affects handling and dynamic stability of the vehicle due to variation of the angles of the wheel and the suspension links (i.e. camber, caster and toe). However these changes cause other problems. In this paper, in conjunction with the study of three-dimensional kinematic model of McPherson mechanism, a set of mathematical equations are derived to determine the suspension behavior of a typical vehicle through the rolling. The kinematic analysis is followed by an optimization process using the genetic algorithm method to determine the optimum length and orientation of the mechanism’s members to minimize the variations of the toe, the camber and the caster angles. However the variations cannot be expressed by closed form functions, thus a performance index is defined in the integral form which expresses the overall variations of the main parameters in the whole range of rolling of the body. It is shown that the genetic algorithm can be effectively used in optimization of three-dimensional behavior of such spatial linkages in which the performances indices have no closed form with many variables under the non-smooth constrains. The presented method not only can be used to design of optimum novel suspension systems, but also to improve the kinematic behavior of existing systems.

In this paper, at first the attenuation of Lamb waves in three-layer adhesive joints, including two elastic plates bonded together by a viscoelastic adhesive layer, is investigated using Global matrix method and then suitable incidence angle is theoretically calculated to generate low-attenuation Lamb waves using angle beam transducer. Theoretical boundary value problem in three-layer adhesive joints with perfect bond and traction-free boundary conditions on their outer surfaces is solved to find a combination of frequencies and modes with lowest attenuation. Characteristic equation is derived by applying continuity and boundary conditions in three-layer joints using Global matrix method. Phase velocity dispersion curves and attenuation intensity plot in high and low frequencies are obtained with numerical solution of this equation by a computer code for a three-layer joint, including an aluminum repair patch bonded to the aircraft aluminum skin by a layer of viscoelastic epoxy adhesive. To validate the numerical solution results of characteristic equation, wave structure curves are plotted for a special mode in two different frequencies in the adhesive joint. Also, transducer incidence angle is calculated in terms of frequency for different modes using theoretical method to generate Lamb wave modes with low attenuation level by angle beam transducer. These modes are recognizable by transducers in inspections with Lamb waves because of low attenuation level.

This paper studies stress distribution in a single-walled carbon nanotube (SWCNT) under internal pressure with various chirality. Strain gradient theory is used to capture the size-dependent behavior of the SWCNT. Minimum total potential energy principle is successfully applied to derive the governing differential equation and its associated boundary conditions. Due to complexity of the governing differential equation and boundary conditions, numerical scheme is used to solve the problem. Comparing the results based on strain gradient theory and that of classical elasticity shows a major difference between these two methods. However, a close examination of the results indicates that both theories predict the same trend for variations in the radial displacement along the SWCNT radius. Numerical results also indicate that the proposed model can lead into the classical elasticity model, provided the material length scale parameters are taken to be zero. Additionally, for plane strain condition, the radial displacements predicted by strain gradient theory are lower than those predicted by classical elasticity theory. Moreover, numerical results show that in a SWCNT, the non-dimensional radial and circumferential stresses along the wall thickness of the SWCNT increase as the radius is increased. The opposite behavior is true for non-dimensional high-order stresses.

The effect of viscoelasticity of epoxy adhesive on creep behavior in the adhesive layer of a double-lap joint is studied in this paper. The joint is comprised of three elastic single isotropic adherend layers joined by an epoxy adhesive that is under shear loading. Prony series is used to modeling the relaxation modulus of epoxy adhesive. The differential equation is derived in Laplace domain, and numerical inversion from the Laplace domain to the time domain is achieved by the Fixed Talbot method. Results show that for an impulse load of 100N, maximum shear stress in the adhesive layer is reduced to 38% of its initial value after almost 12 days and 79% of its initial value over a very long time. The rate of increase in tensile load P has a direct effect on peak shear stress developed in the adhesive layer and holding P0 as a constant, increasing t p will lower the induced peak shear stress in the joint. Also, an increase in the thickness of the adhesive layer reduced the induced peak shear stress and strain in the joint.

At present, tend to use of FW composite pipes is increasing in different industries and structures. FW composite pipes made of fiber-reinforced plastics have many potential advantages over pipes made from conventional materials, such as high specific stiffness and strength, good corrosion resistance and thermal insulation [1]. With the development of manufacturing technology to produce FW pipes, there has been a growing interest in application of the FW fiber-reinforced cylindrical composite structures [2]. Numerous studies, including bending [3], transverse loading [4], axial compression [5], and internal pressure loading conditions [6], has been conducted on the mechanical properties and Failure of FW pipes. The elasticity solution of isotropic cylindrical shells subjected to uniform radial linear loads has been studied by Klosner et al. [7]. Based on the solution of Lekhnitskii [8], Wild and Vickers [9] have developed an analytical procedure for the orthotropic cylindrical sheets. Xia et al. [6] have developed an analytical procedure to assess the multilayered FW composite pipes under internal pressure. Also, other people such as Wahab [10], Bakaiyan [11] and Ansari [12] have done extensive research in various load conditions on composite pipes. Laney [2] has described the use of composite pipe materials in transportation of natural gas. Note that natural gas is dangerous and incendiary material, so you can use a substance for preventing the spread of fire. Mouritz [13] has introduced the Carbon-Epoxy as the most often used composite in load-bearing aircraft structures, which is flammable and readily decomposes when exposed to heat and fire. Funucci [14] has reported that the thermal conductivity of a solid char at room temperature is 0.17 Wm−1 K−1, whereas the in-plane conductivity for a virgin carbon-epoxy laminate is so higher at about 8–12 Wm−1 K−1, depending on fiber content. Low density and highly porous chars tend to provide the best thermal insulation [13].

When the size of structures approaches to the sub-micron scale, physical responses of such systems become size-dependent, hence, classic theories may not be able to predict the behavior of the miniature structures. In the present article, the modified couple stress theory (MCST) is employed to account for the effect of the size-dependency on the dynamic instability of torsional nano-electromechanical systems (NEMS) varactor. By incorporating the Coulomb, Casimir and damping forces, the dimensionless governing equations are derived. The influences of Casimir force, applied voltage and length scale parameter on the dynamic behavior and stability of fixed points are investigated by plotting the phase portrait and bifurcation diagrams. It is found that the Casimir force reduces the instability threshold of the systems and the small-scale parameter enhances the torsional stability. The pull-in instability phenomenon shows the saddle-node bifurcation for torsional nano-varactor.

Using GDQ method, the radial and circumferential stresses in an annular FGM plate with a uniform thickness under a transverse axisymmetric load is investigated. It is assumed that a uniform radial magnetic field acts on the top surface of the plate. The modulus of elasticity E and the magnetic permeability coefficient μ of the plate along its thickness are assumed to vary according to the volume distribution function. The Poisson's ratio ν is considered to be constant. Based on the classical plate theory (CPT), equilibrium equations are deduced and the displacement fields are determined. The radial and circumferential stresses as well as transverse and radial displacements are obtained accordingly. The effect of volume fraction function power m on the maximum deflection in the absence and presence of the magnetic field is also investigated. Moreover, the effect of t/a and b/a ratios on displacements, stresses, induction magnetic field intensity and the resulting Lorentz force are also investigated. According to the results, for different points along the radial direction, the application of radial magnetic field to the top surface of the plate completely changes the state of stress in both tangential and radial directions, resulting in tensile and compressive stresses in these two directions. The results also indicate that in presence of magnetic field, the plate displacement and stress components are lowered considerably.